A passive optical network (PON) is a system for providing network access over the last mile, which is the final portion of a telecommunications network that delivers communication to customers. A PON is a point-to-multipoint (P2MP) network that comprises an optical line terminal (OLT) at a central office (CO), an optical distribution network (ODN), and optical network units (ONUs) at customer premises. PONs may also comprise remote nodes (RNs) located between the OLTs and the ONUs, for instance at the end of a road where multiple customers reside.
In recent years, time-division multiplexing (TDM) PONs such as gigabit-capable PONs (GPONs) and Ethernet PONs (EPONs) have been deployed worldwide for multimedia applications. In TDM PONs, the total capacity is shared among multiple users using a time-division multiple access (TDMA) scheme, so the average bandwidth for each user may be limited to below 100 megabits per second (Mb/s).
Wavelength-division multiplexing (WDM) PONs are considered a promising solution for future broadband access services. WDM PONs may provide high-speed links with dedicated bandwidth up to about 10 gigabits per second (Gb/s). By employing a wavelength-division multiple access (WDMA) scheme, each ONU in a WDM PON is served by a dedicated wavelength channel to communicate with the CO or the OLT.
Next-generation PONs (NG-PONs) and NG-PONs stage 2 (NG-PON2s) may include point-to-point WDM PONs (P2P-WDM PONs) and time- and wavelength-division multiplexing (TWDM) PONs, which may provide data rates higher than 10 Gb/s. TWDM PONs combine TDMA and WDMA to support higher capacity so that an increased number of users may be served by a single OLT with sufficient bandwidth per user. In a TWDM PON, a WDM PON may be overlaid on top of a TDM PON. In other words, different wavelengths may be multiplexed together to share a single feeder fiber, and each wavelength may be shared by multiple users using TDMA.